1. Field of the Invention
The invention relates to communication cables, such as electrical and optical communication calbes and cable connectors and somewhat more particularly to a sealing material for longitudinal sealing of electrical and optical communication cables and cable connectors.
2. Prior Art
In order to prevent longitudinal spreading of water or dampness in communication cables, such as electrical or optical communication cables, which have leads insulated with a synthetic material, the cable core is filled with a water-repelling or water-absorbing, expanding material. For example, cellulose-like materials which increase in volume by a multiple upon contact with water, as well as expandable polyurethanes are known (for example see German OS No. 2,361,207). Likewise, petrolatum-like materials are also useful for such functions. Further, in optical communication cables, having transmission elements composed of glass fibers, petrolatum-like materials also function to assure the mobility of the transmission elements within the cable core (for example see German OS No. 2,302,662, which approximately corresponds to U.S. Pat. No. 4,072,398; or German OS No. 2,429,670 which approximately corresponds to British Patent Specification No. 1,445,732).
In order to expel water from a cable core of a communication cable and to prevent any further penetration of water therein, a sealing compound comprised of a polyol, an isocyanate-prepolymer, a gelling material and a catalyst are known. Over a relatively long period of time, such originally liquid material is converted into a soft, sticky compound which moistens the insulation layers about cable leads. Such sealing material essentially comprises a solution of a liquid urethane elastomer that reacts at room temperature in a relatively low viscosity oil. In this manner, a urethane elastomer is formed from a polyol and an isocyanate-prepolymer. Such polyol generally comprises a polyester, a polyether or caster oil. In formulating such sealing material, the polyol and isocyanate-prepolymer are dissolved in an aromatic solvent and a catalyst, such as dibutyl tin dilaurate is added whereby the urethane is formed (for example, see German OS No. 2,259,411, which approximately corresponds to U.S. Pat. No. 3,733,426).
In longitudinal sealing of communication cables, specific conditions must sometimes be taken into consideration for certain applications. For example, this is a case when a communication cable is utilized in a pressure environment wherein the cable core is subjected to an axial gas pressure during operation. In such an application, it is necessary to prevent the formation of uninterrupted gas channels in the longitudinal direction of the cable because such gas channels cause the migration of individual components with the cable core.
Similar conditions are required for cable connectors, such as, for example, cable sleeves. Thus, in connecting two communication cables, it is necessary to splice the lead bundles opened from each cable and to connect them with the leads of the other cable. The individual leads connected in such a manner must be insulated from the surrounding environment and from one another so that a structure forms which is significantly larger than the original cable, in terms of space. Further, since the insulation of the individual leads was opened during splicing, the connected structure must also be protected against moisture.
The art is aware that cable connectors and other cable devices can be filled with casting compounds, for example see British Patent Specification No. 1,157,435.